Transformer Neutral Earthing as per IEC 1

[NickParker]

I have a question regarding transformer neutral earthing in IEC land,
(1): Should the transformer Neutral and the transformer frame along with other substation equipment's/structures be interconnected and earthed in substation? or
(2): Should the transformer neutral and the frame be separately earthed and brought to the Main switchboard and interconnected via Link only at the Main switchboard? The neutral and the earth is not connected anywhere else.

I have seen lot of earthing done as per (1) and it seems (2) is also followed in some countries. My question is which one is the correct way of doing it?

 

[prc]

I think (1) is appropriate. During an LG fault, neutral to earth will carry full fault current and why should it be taken to the main switchboard? In my view neutral earthing and equipment grounding should be done separately and not to be interconnected.

 

[RRaghunath]

Equipment earthing and system earthing are maintained distinct right up to the earth pits.
Earth electrodes are interconnected below the ground.

R Raghunath

 

[che12345]

I have the following opinion for your consideration.
1. I think No.1 is better. That is transformer Neutral and the transformer frame along with other substation equipment's/structures be interconnected and earthed in the substation. Where the Main switchboard is earthed separately. Any Line to Earth fault at the Mainboard, the fault current flows from Main switchboard earthing to the earth, to the sub-station earthing, to the Trafo Neutral. There is no fault current flowing through the Neutral line.
2. No.2 : a) at the substation, the Trafo Neutral and frame are earthed separately is wrong.
b) at the Main switchboard, any Line to Earth fault would have two separate paths, i.e. one through the earth and another through the Neutral line. This is wrong. The Neutral should NOT be involved to carry the earth-fault current.
Che Kuan Yau (Singapore)

 

[7anoter4]

In my opinion, the transformer neutral and the transformer tank grounding are two separate problems.
The grounding of the tank is connected with substation EPR [GPR] and the neutral is connected with the grounding fault current. So, the tank has to be grounded directly to the grounding grid.
The neutral may be connected [or not] to the grounding system as per system phase-to-ground fault policy. Usually, the system coordinator will state if the neutral will be connected directly or through a neutral transformer, resistance, inductance or else.

 

[che12345]

I have the following opinion.
1. "In my opinion, the transformer neutral and the transformer tank grounding are two separate problems".
I agreed in full.
2. Earthing of trafo Neutral and tank may be in different configurations.
2,1 Trafo with Neutral solidly earthed:
Trafo iron core is connected to the tank. Tank, Neutral and conductive structure should be connected to the Earthing bar. An earthing conductor from earthing bar to the earthing-rod, which is in contact with the earth (soil). The tank and the Neutral should NOT be earthed separately.
2.2 Trafo with Neutral impedance earth:
Trafo Neutral should be connected to the impedance say No.1 . Impedance the other end to the Earthing bar. Trafo iron core is connected to the tank. Tank and conductive structure should be connected to the Earthing bar. An earthing conductor from earthing bar to the earthing-rod, which is in contact with the earth (soil). Only the tank + structure are solidly earthed.
2.3 Trafo with Neutral floating:
Trafo Neutral may be distributed supplying single phase loads, is "floating" i.e. NOT connected to the impedance or earthed. Trafo iron core is connected to the tank. Tank and conductive structure should be connected to the Earthing bar. An earthing conductor from earthing bar to the earthing-rod, which is in contact with the earth (soil). Only the tank + structure are solidly earthed.
Che Kuan Yau (Singapore)